Question: Solve for $x$ and $y$ using substitution. ${-2x-y = -3}$ ${y = x+9}$
Explanation: Since $y$ has already been solved for, substitute $x+9$ for $y$ in the first equation. ${-2x - }{(x+9)}{= -3}$ Simplify and solve for $x$ $-2x-x - 9 = -3$ $-3x-9 = -3$ $-3x-9{+9} = -3{+9}$ $-3x = 6$ $\dfrac{-3x}{{-3}} = \dfrac{6}{{-3}}$ ${x = -2}$ Now that you know ${x = -2}$ , plug it back into $\thinspace {y = x+9}\thinspace$ to find $y$ ${y = }{(-2)}{ + 9}$ $y = 7$ You can also plug ${x = -2}$ into $\thinspace {-2x-y = -3}\thinspace$ and get the same answer for $y$ : ${-2}{(-2)}{ - y = -3}$ ${y = 7}$